Generally, when a lithium ion battery, that is, a rechargeable battery, is overcharged to a predetermined voltage or more, it may explode or ignite. Further, a battery pack typically includes a plurality of battery cells to obtain required output. When at least one of battery cells included in the battery pack is overcharged and explodes or ignites, other battery cells, as well as the overcharged battery cell, are also influenced by such overcharge, and thus it is essentially required to prevent the overcharge of a battery in order to secure the safety of the battery.
In conventional technology, there is a method for, when the voltage of a battery cell increases due to overcharge, sensing an overvoltage and turning off a relay in a power relay assembly (PRA), thus blocking the overcharge of the battery. However, this method is problematic in that, when the relay is shorted, it cannot be turned off, thus making it impossible to prevent overcharge.
The patent document described in the following Prior Art Documents discloses technology in which, when swelling occurs in a battery cell due to overcharge, a control unit 160 melts and blows a fuse 300, thus blocking charging/discharging current of a battery pack. Referring to FIG. 1 of the following patent document, when swelling occurs in a battery cell 200, a first pole plate 100 attached to the external material of the cell and a second pole plate 120 attached to an electrode assembly are spaced apart from each other by a predetermined distance, and the first pole plate 110 and the second pole plate 120 act as a capacitor due to an electrolyte filled between the external material of the cell and the electrode assembly. A phase difference sensing unit 150 senses a phase difference between a current and a voltage, and determines that swelling has occurred in the cell 200 due to overcharge when the phase difference is about 90°, and thus the control unit 160 blocks the charging/discharging current of the battery pack by melting and blowing the fuse 300.
However, the following patent document is problematic in that complicated multiple components, such as the first pole plate 110, the second pole plate 120, a resistor unit 140, an Alternating Current (AC) power supply unit 130, the phase difference sensing unit 150, and the control unit 160, must be added, thus complicating the configuration and increasing manufacturing cost.
Therefore, there is required an apparatus for preventing battery overcharge, wherein there is no need to add a function of preventing overcharge to a control unit by using only passive elements, and which has such a simple configuration that the apparatus can be added to the sensing circuit of the battery cell, and which can secure additional safety of the battery by blocking a voltage applied to a battery cell in a battery module when overcharge occurs.